In one tank car construction commonly used, a valve cage or guide is located in the bottom of the tank adjacent an opening in the tank bottom. A lading valve is movable vertically relative to the tank bottom opening between open and closed positions. An operating rod for the lading valve extends through the valve cage to the top of the tank. The valve cage guides vertical movement of the operating rod as the lading valve moves between open and closed positions. The operating rod may be provided with a pin and slot arrangement to allow vertical movement of the tank top relative to the tank bottom and allow a small amount of misalignment. The valve cage and the valve operator may be cooperatively threaded whereby the lading valve rotates in moving vertically between open and closed positions. See, for example, U.S. Pat. Nos. 1,605,460 and 1,727,702.
In one bottom operated lading valve construction disclosed in U.S. Pat. No. 3,981,481 (Sept. 21, 1976) a lading valve is movable vertically relative to a valve seat formed on a valve body located in the bottom of the tank. An outlet housing or chamber is attached to a flange portion of the valve body with fasteners which define a shear plane. The housng includes a lower operator extending vertically within the housing which engages an upper operator located within the valve body to move the lading valve between open and closed positions. In the event of hard impact to the housing, for example in a derailment, the housing will shear off along the shear plane defined by the fasteners and the lower operator will shear off or drop off from the upper operator, leaving the lading valve in place to substantially prevent the escape of lading.
In U.S. Pat. No. 3,486,528 (1969), a bottom operated air vent valve operator includes ball and socket joints to allow for misalignment of the vertical operator relative to the tank top valve seat 18. However, this operator is a push-pull type and these ball and socket joints will not transmit torque.
Universal joints which will transmit torque and which allow for longitudinal misalignment are commercially available. For example see Lovejoy Products, Publication No. L1005 (dated Feb. 1977) 2655 Wisconsin Ave., Downers Grove, Ill. 60615.